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I would be curious how these were formed. Was it somehow folded onto itself in a forging process which left a void?

John Molloy - you are the real metallurgist here, I'm just an armchair hack with a few classes and labs (and plenty of experience breaking things) - does it look like this was a void that created a weak area to you? That would be my guess looking at the picture without getting it in hand with a magnifying glass or scope.

-Michael
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http://www.bigblockmopar.nl/test/IMG_3692.JPG






Mike! 'Sup!

I'm no more a metallurgist than you are a mechanical engineer. Speaking of which, I always try to consider the stress state that would drive a crack. This one is a little more complicated since it's dynamically loaded, and even if there was a weird bending moment due to lack of preload and pot holes, it still can't explain the orientation of the vast majority of the fracture surface. At least not to me. Maybe a mechanical engineer can clear it up?

Not a forging expert either, but I do know that there are lots of bad things that can happen in a forging process. If it was possible to do metallography of a cross section we could probably put this to bed.

PHJ426, yeah I see it, and can't explain it. What would really clinch this is if you could find paint in the opened crack. We routinely open cracks by back cutting and then using cryogenics to assist (at least for most steels). Paint in the opened crack, even the tiniest amount, infers pre-existing defect.